PCMag’s Sascha Segan has created a slideshow comparison of iPad apps and Android tablet apps. The more enthusiastic you are about the potential of Android tablets, the more distressing the show is: with one or two exceptions, the Android examples are just plain dismal. Mostly, they’re Android phone apps –some of which aren’t that hot in the first place — which have merely been stretched for a tablet-size screen, leaving a vast wasteland of white space.

In February of 2011, I attended the event at which Google unveiled Honeycomb, the first truly tablet-friendly edition of Android. I came away assuming that the company’s efforts would jump-start the market for Android tablet software. Even if the iPad retained a very comfy lead in app quantity and quality, I thought, Android would achieve clear momentum as a tablet platform. Just like it did with smartphones.

Wrong!

I don’t claim to understand for sure why the Android tablet app situation remains so depressing. But I do have some theories. Nine of them, actually:

1. Google doesn’t understand that apps are important. In its heart, it’s a believer in a web-centric universe, not an app-centric one. (That’s the instinct that led the company to invent Chromebooks.) If you think of apps as an inconvenience or a stopgap, you’re less likely to take them seriously — which is a dangerous scenario if you spearhead an important app platform.

2. Google thinks stretchy apps are a pro, not a con. I remember back to when Samsung’s first Galaxy Tab was new. Google employee Tim Bray — a smart guy — said that the app situation was “amazingly good,” based in part on the ability of phone apps to expand themselves to tablet size. By now, I hope, it’s clear that tablets want apps that were written to work well on tablets. Especially big-screen tablets such as most of the major Android contenders. The fact that there’s no standard resolution for Android tablets doesn’t help: There’s no way to design a single pixel-perfect interface, as you can do with an iPad program.

3. Google isn’t good at getting developers excited about Android tablets. There’s certainly plenty of evidence that software companies are interested in partnering with Google in general. (Its upcoming I|O developer conference just sold out — in 20 minutes.) But maybe Google simply hasn’t made a convincing case to enough programmers that it’s worth their while to take Android tablets seriously. (By contrast, Microsoft, which knows as much about courting developers as any company on the planet, has spurred the creation of 70,000 Windows Phone apps to date — pretty impressive for a platform that hasn’t caught on with consumers yet. And many Windows Phone apps are nicely done.)

4. Developers are smart. Why bother to invest your energy in a tablet platform that’s off to a sluggish start when you can concentrate on the thriving iPad market?

5. Developers are dumb. Some of the apps which Segan shows look so crummy on Android tablets that they can’t be good for the reputations of the companies who released them. And they certainly aren’t good for the reputation of Android tablets.

6. It’s just a chicken-and-the-egg scenario. Consumers will flock to a platform if they know it has great apps. Developers will flock to it if they see vast numbers of potential customers. Android tablets, with neither the apps nor the large customer base, are stuck in limbo.

7. Google has a plan — it’s just not talking about it yet. Back in December, Google Chairman Eric Schmidt said that the developers who emphasize Apple’s iOS over Android would reverse their stance within six months. Schmidt’s notorious for making apparently ill-advised predictions, but he knows more about Google’s plans for Android tablets than I do. Perhaps he’s being rationally exuberant.

8. The relative health of the Android smartphone app market is a fluke. Android is a hit on smartphones in part because wireless carriers are smitten with it. They’ve worked hard to put handsets in the hands of hundreds of millions of consumers, creating a large customer base for developers. The tablet market doesn’t work that way: nothing will happen without a lot more heavy lifting on Google’s part.

9. A little bit of all of the above. That’s the most likely explanation, isn’t it?

If you’re rooting for Android tablet apps to provide serious competition to the iPad, it’s too early to give up hope. It’s easy to forget that Android smartphones weren’t insta-hits, either: for about a year after the platform debuted in 2008, it wasn’t entirely clear whether it would go anywhere. Then it did. Rapidly.

Still, when I attend Google I|O in June, I’m going to be looking for evidence that Google is acknowledging that the paucity of good Android tablet apps is a problem, and that it has a solution in mind.

If it doesn’t? Then I’ll panic — or at least divert my attention to Windows 8.